Artemisia arbuscula subspecies longiloba is known from about 17 locations in the very southern portions of Beaverhead, Madison, and Park Counties. While the range of subspecies longiloba appears limited within Montana, its presence does not suggest rarity. Current information on this plant's locations, population sizes, and threats are greatly needed.

In Montana we have subspecies arbuscula and longiloba (refer to Habitat, Phenology & Diagnostic Characteristics).

Phenology

Subspecies arbuscula flowers from mid- to late summer (FNA 2006), which in Montana is mid-August to September (Lesica 2012).

Subspecies longiloba flowers from early to late spring (FNA 2006), which in Montana is from July to mid-August (Lesica 2012). Its ability to begin blooming as snow melts in the spring is a unique characteristic for the subgenus Tridentatae (FNA 2006).

In Montana subspecies arbuscula has been found in Beaverhead, Gallatin, Madison, and Park Counties (http://www.pnwherbaria.org). Its range includes California, Colorado, Idaho, Montana, Nevada, Utah, Washington, and Wyoming.

In Montana subspecies longiloba has been found in Beaverhead, Madison, and Park Counties (MTNHP 2018 botany database). Its range includes California, Colorado, Idaho, Montana, Oregon, Utah, and Wyoming.

(Observations spanning multiple months or years are excluded from time charts)

Habitat

Subspecies arbuscula plants are found in rocky sedimentary soils in high valleys and mountain slopes at elevations from 1500 to 3800 meters (FNA 2006). In Montana plants occur on stony calcareous soil (Lesica 2012).

Subspecies longiloba plants are found on clay soils of alkaline basins and valleys, occasionally on outwash plains of mountains, at elevations from 1500 to 2500 meters (FNA 2006). In Montana plants occur on fine-textured soil of stream terraces (Lesica 2012).

Ecology

Artemisia arbuscula ssp. longiloba may be heavily browsed in winter where there is little snow cover (Boyle and Reeder 2005). This taxon is tolerant of saturated soils in spring and dry periods in summer and fall (Boyle and Reeder 2005).

Reproductive Characteristics

Artemisia arbuscula flowers (heads): The involucre is campanulate, about 2–5 mm high with green, tomentose phyllaries (Lesica 2012). The receptacle is glabrous. Heads consist of 4-8 perfect (contains both male and female structures) disk flowers that are glabrous or glandular; corolla is about 2 mm long (Lesica 2012). Achenes are resinous and less than 1 mm long (Lesica 2012).

The involucres for subspecies arbuscula are 3.5-4 mm tall and 2-4.5 mm in diameter (FNA 2006).

The involucres for subspecies longiloba are 2-3 mm tall and 1.5-2.5 mm in diameter (FNA 2006).

Kartesz, J.T. 2015. The Biota of North America Program (BONAP) North American Plant Atlas. Chapel Hill, N.C. [maps generated from Kartesz, J.T. 2015. Floristic Synthesis of North America, Version 1.0. Biota of North America Program (BONAP). (in press)].